fix: allow exiting a running measurement

[radulucut]

Closes #181

[coderabbitai]

Walkthrough

Signal handling for SIGINT and SIGTERM is redistributed across commands. The centralized signal handling previously in root.go—which imported os/signal and syscall—is removed. Signal registration is now implemented independently in auth.go and ping.go, allowing each command to manage cancellation of its respective flow upon receiving OS signals.

Pre-merge checks and finishing touches

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description references the linked issue #181, which relates to the changeset's objective of enabling interruption of running measurements.
Linked Issues check	✅ Passed	The changes implement OS signal handling (SIGINT/SIGTERM) in auth.go and ping.go to enable measurement cancellation, directly addressing issue #181's requirement for Ctrl+C interruption.
Out of Scope Changes check	✅ Passed	Removal of signal handling from root.go is necessary to avoid duplicate signal registration, making it an in-scope refactoring supporting the signal handling consolidation in auth.go and ping.go.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title accurately describes the main objective of the PR: enabling users to exit running measurements via Ctrl+C by adding OS signal handling.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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